No. 586] THE INHERITANCE OF D UBLENESS 



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it in five genera representing as many distinct orders. 

 Bateson himself (1909, chap. 9) reports a fact which 

 seems to exclude it in the sweet pea, although his redu- 

 plication hypothesis 6 (Bateson and Punnett, 1911) would 

 require it there if anywhere. 



This phenomenon is one to which East (1915, p. 87) has 

 recently referred, the ' ' zygotic ' ' nature of certain pol- 

 len-grain characters. In the sweet pea. for instance, F t 

 hybrids between certain races with long (dominant) and 

 round pollen have the pollen all long, although segrega- 

 tion, on any hypothesis, must have already occurred 

 before the shaping of the pollen-grains. If segregation 

 takes place as a result of chromosome-reduction, in the 

 formation of the spore-tetrads, it is not strange that the 

 cytoplasm of the young pollen-grain still retains the im- 

 press of the diploid maternal set of chromosomes, so that 

 the pollen-grains give no evidence in their shape of the 

 segregation that has just taken place. On the other 

 hand, if segregation takes place early enough to permit 

 of extensive " reduplications " of the cells carrying cer- 

 tain combinations of factors, it is very strange that the 

 cytoplasm of the pollen-grain should be essentially 

 maternal in nature. Especially does this evidence nega- 

 tive any hypothesis of cytoplasmic segregation— and if 

 segregation is nuclear, surely we have reasons enough for 

 connecting it with the reduction of the chromosomes. 



It is due to Goldschmidt's hypothesis to note that a 

 factor " completely coupled " with S, completely lethal 

 for pollen and only slightly so for the embryo-sac, would 

 explain the peculiarities of the case in Matthiola, both the 

 non-functioning of the S-carrying pollen and the excess 

 of doubles over 50 per cent. This is an amplification of 

 his suggestion, in a passing reference (1913, p. 81), of a 



hypothesis of somatic segregation. Tli'oy iissiun,. th.it a period of cell-divi- 



